Domestic Uses of Electricity and AC/DC — AQA GCSE Physics
Mains electricity is alternating current; cells and batteries provide direct current.
Alternating and direct current
- Direct current (d.c.) flows in one direction only. It is provided by cells and batteries.
- Alternating current (a.c.) repeatedly changes direction. It is produced by a.c. generators and is what the mains supplies.
UK mains supply
The UK mains supply is alternating current with:
- a frequency of 50 Hz (it changes direction 50 times per second), and
- a potential difference of about 230 V.
The three wires
A three-core cable has:
- Live (brown) — carries the alternating p.d. (~230 V), the dangerous wire.
- Neutral (blue) — completes the circuit, around 0 V.
- Earth (green and yellow) — a safety wire that only carries current if there is a fault.
Why a.c. for mains?
Alternating current is used for the mains because it can be easily transformed to different voltages using transformers, which makes efficient transmission through the National Grid possible.
Exam tips
- d.c. = one direction (cells/batteries); a.c. = changes direction (mains, generators).
- UK mains: a.c., 230 V, 50 Hz.
- Learn the three wires by colour and role.
- a.c. is used for mains because it can be transformed to other voltages.